A Discourse 

on  the 

Chemistry  of  Artists'1  Paints 

Vehicles  and  Varnishes 


Held  at 

The  Art  Students  League  of  New  York 

and  at  the 

Pennsylvania  Academy  of  Fine  Arts,  Philadelphia 


1922-1923 


By  F.  W.  WEBER 

Technical  Director  of  F.  Weber  Co. 
Manufacturing  Artists’  Colormen  Since  1854 
Philadelphia,  Pa. 


A DISCOURSE  ON  THE 


CHEMISTRY  OF  ARTISTS  PAINTS,  VEHICLES 
AND  VARNISHES 

Held  at  The  Art  Students  League  of  New  York  and  at  the 
Pennsylvania  Academy  of  Fine  Arts,  Philadelphia 

1922-1923 

By  F.  W.  WEBER 

Technical  Director  of  F.  Weber  Co.,  Philadelphia,  Pa.,  Manufacturing  Artists 
Colormen  Since  1854 

The  study  of  the  composition  and  chemistry  of  Artists’  colors, 
vehicles  and  varnishes  which  today  is  of  such  importance,  is  unfor- 
tunately only  too  frequently  neglected  by  the  student  and  Artist. 
It  is  not  necessary  that  the  Artist  become  a color  chemist,  but  a 
practical  technical  knowledge  will  greatly  aid  in  assuring  permanent 
and  durable  results,  when  the  lack  of  same  often  proves  of  serious 
embarrassment,  sometimes  even  during  the  Artist’s  own  lifetime. 

It  is  only  within  comparatively  recent  time  that  the  manufacture 
of  Artists’  colors  began  as  an  industry.  Before  this  time  the  painter 
prepared  his  own  products  and  no  doubt  welcomed  the  commercial- 
izing of  this  phase  of  his  art.  This  severance  of  course  was  inevita- 
ble, due  to  the  rapid  progress  of  chemistry  as  a science,  whereby  an 
unlimited  number  of  pigments,  etc.,  began  to  elaborate  the  Artist’s 
selection.  Today  the  student  may  choose  from  such  a variety,  that 
not  to  run  into  difficulties  would  almost  be  a miracle. 

The  ideal  way  to  relieve  the  Artist  of  most  dangers  would  be 
to  appoint  a commission  composed  of  Artists  and  technical  men.  I 
understand  there  are  such  commissions  abroad,  who  publish  the 
result  of  their  decisions  in  pamphlet  form  for  the  Artist.  In  fact, 
I believe  the  time  will  eventually  come  when  such  a commission  will 
be  by  national  appointment,  as  a necessary  means  to  preserve  art. 
The  object  of  such  a commission  would  be: 

i.  To  carefully  look  into  the  quality  of  paints,  vehicles,  var- 
nishes and  sundry  products  offered  to  the  artist  with  which 
a lasting  work  of  art  is  to  be  created.  A guarantee  of  per- 
manence and  durability,  thereby  eliminating  any  loss  of 
vitality  by  the  Artist  in  worrying  over  his  materials. 


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2.  To  work  toward  the  end  of  compelling  all  manufacturers  to 
truthfully  label  all  their  products.  To  prevent  such  misrep- 
resentations as  labeling  inexpensive  or  dangerous  substitutes 
with  the  names  of  the  products  they  imitate.  Establish  na- 
tionally recognized  nomenclature,  to  which  all  products  must 
conform. 

3.  To  consider  technical  questions  affecting  painting  as  a whole 
in  all  its  phases  and  diffuse  such  knowledge  among  Artists. 

In  absence  of  such  a commission  the  Artist  should  not  hesitate 
to  put  these  questions  directly  up  to  the  manufacturer. 

The  future  will  unquestionably  see  the  buyer  of  paintings  de- 
manding to  know  the  palette  of  the  Artist.  Both  the  art  collector 
and  art  speculator  cannot  afford  to  be  anything  else  but  seriously 
interested  in  the  durability  and  permanence  of  modern  art  creations. 

The  Artist  of  the  seventeenth  and  early  eighteenth  centuries  was 
undoubtedly  the  most  unfortunate.  Chemistry  about  this  time  began 
to  develop  as  a science,  and  during  the  ensuing  years  rapidly  pro- 
duced an  exceedingly  large  number  of  many  brilliant,  but  unfor- 
tunately also  many  unsafe  colors,  which  during  their  introduction 
were  mostly  offered  very  impure.  The  Artist  welcomed  the  addition 
of  such  a variety  to  his  palette  and  was  necessarily  forced  to  select 
by  standards  of  brilliancy  only.  We  also  find  that  many  colors 
appeared  under  several  names,  each  manufacturer  striving  to  have 
the  pigment,  or  a modification  of  it,  appear  as  a specialty  of  his  own. 
For  example,  Prussian  Blue,  which  was  discovered  by  Diesbach  in 
1704,  became  known  as  Paris  Blue,  Berlin  Blue,  Bronze  Blue,  Min- 
eral Blue,  Chinese  Blue,  Milori  Blue,  and  lately  also  as  American 
Blue. 

Even  today  many  dangerous  pigments  are  offered  under  fanciful, 
misleading  names,  which  are  meaningless  and  only  too  often  cause 
the  unsuspecting  Artist  to  fall  into  serious  difficulties.  The  ideal 
nomenclature  of  pigments  would  perhaps  be,  to  express  the  chemical 
composition,  which,  however,  would  not  be  very  practical  when 
naming  pigments  of  organic  origin,  these  mostly  being  of  very  com- 
plex composition  with  correspondingly  lengthy  names. 

Pigments,  in  order  to  be  classed  as  such,  must  be  permanent  to 
light,  air,  moisture,  gases,  chemically  indifferent  toward  each  other 
in  mixtures  and  not  suffer  incalcuable  alteration  in  hue  in  any 
technique.  All  durable  pigments  should  also  be  insoluble  in  water 


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or  alcohol.  By  being  permanent  to  light  is  presupposed  to  mean  that 
the  pigment  be  absolutely  permanent  under  ordinary  diffused  light, 
as  also  show  complete  stability  when  exposed  to  direct  sunlight. 

The  student  generally  supposes  light  to  be  the  worst  enemy  of 
permanence,  which  usually,  however,  is  not  as  serious  as  climate 
variances  in  temperature  and  atmospheric  influences.  Only  seldom 
is  a painting  exposed  to  strong  sunlight  for  any  length  of  time,  but 
impure  air,  gases  and  moisture  come  in  constant  contact  with  the 
majority  of  pictures  even  in  some  of  our  largest  galleries.  A great 
many  of  the  old  masterpieces  owe  their  destruction  to  disintegration, 
caused  by  the  constant  condensation  and  evaporation  of  moisture  on 
their  surface,  which,  carried  on  over  an  indefinite  period,  together 
with  the  action  of  impure  air,  contaminated  with  sulphurous  gases, 
etc.,  gradually  brought  about  changes,  which  were  impossible  for 
light  alone  to  have  accomplished.  At  a later  lecture  the  subject  of 
cracking,  fading,  wrinkling,  etc.,  and  their  prevention,  will  be  inti- 
mately discussed. 

Pigments  may  be  divided  into  two'  classes : 

f Natural , such  as  the  Ochres. 

Mineral  j Artificial , such  as  the  Cadmium  Yellows,  Cobalts, 
(.  Vermilion,  Emeraude  Green. 

(Vegetable , such  as  Madder  Lakes,  Gamboge, 
Indigo. 

■Animal,  .such  as  Sepia,  Indian  Yellow,  Carmine. 
Artificial,  such  as  Alizarin  Lakes. 

The  natural  and  artificial  mineral  pigments  represent  the  most 
important  group,  as  it  is  from  this  group  that  the  most  desirable 
pigments,  are  obtained.  From  the  natural  mineral  group  the  Old 
Masters  obtained  most  of  their  colors,  but  today  the  colorman  selects 
a large  number  of  his  best  products  from  the  artificial  mineral  group. 
Of  least  importance  to  the  Artist  are  the  pigments  of  organic  origin, 
among  which  the  Madder  Lakes,  Indigo,  Gamboge  are  perhaps  the 
best  from  vegetable  source.  The  many  yellow  lakes,  such  as  Italian 
Pink,  Dutch  Pink,  Brown  Pink,  etc.,  derived  also  from  this 
source,  are  of  little  importance  owing  to  their  fugitive  character 
to  light  and  instability  in  mixtures  with  many  metallic  pigments  such 
as  the  White  Leads,  Chrome  Yellows,  etc.  Sepia,  Indian  Yellow, 
and  Carmine  are  the  most  important  of  those  from  animal  source. 
All  three  may  be  easily  dispensed  with ; especially  do  I wish  to  warn 
the  Artist  against  the  use  of  Carmine.  This  pigment,  although  of 


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such  brilliance  and  individuality  of  hue,  is  very  fugitive  to  light  and 
readily  decomposed  in  mixture  with  many  metallic  pigments,  such 
as  White  Leads,  Chrome  Yellows,  Yellow  Ochres,  etc.  Being  an 
expensive  color,  it  may  be  easily  replaced  by  the  very  desirable 
Alizarine  Madder  Lakes. 

The  artificial  organic  pigments  unquestionably  furnish  a large” 
number  of  pigments  than  all  other  groups.  Since  the  accidental 
discovery  of  Mauve  from  aniline  (a  coal-tar  derivative)  in  1856  by 
the  English  chemist  Perkins,  which  formed  the  starting  point  for 
the  inconceivable  number  of  dyes  developed  since  then,  most  of  the 
lake  pigments  produced  with  these  dyestuffs  unfortunately  prove  far 
too  fugitive  for  use  as  Artists’  pigments.  The  exception  in  this  in- 
stance being  the  very  permanent  Alizarine  Lakes,  derived  from  an- 
thracene, which  is  also  a coal-tar  derivative. 

I have  found  that  many  artists  are  of  the  opinion  that  the 
Alizarine  Lakes  are  aniline  colors.  The  fact  that  aniline  and  also 
anthracene  are  both  derivatives  of  coal-tar  should  not  lead  the  Artist 
to  believe  that  the  colors  obtained  from,  these  products  are  identical  in 
their  properties.  The  aniline  derivatives  such  as  Mauve,  Magenta, 
etc.,  are  not  desirable  owing  to  their  instability  and  lack  of  perma- 
nence, but  the  Alizarine  Lakes  are  chemically  a different  class  of 
compounds  and  are  very  desirable,  possessing  high  stability  and 
permanence. 

We  have  spoken  above  of  Lake  colors  and  I think  it  may  be  of 
sufficient  interest  to  describe  such  a product.  The  derivation  of  the 
name  lake  is  said  by  Pliny  in  his  Naturalis  Historia , A.  D.  77,  to  be 
from  the  lac,  or  coloring  principal,  of  insect  origin,  used  by  the  early 
Italian  dyers.  In  conjunction  with  compounds  of  tin  and  aluminum 
the  dye  was  precipitated  and  fixed  indelibly  on  the  fabric.  During 
the  process  of  dyeing  some  of  the  lac  combines  with  some  of  the  tin 
and  aluminum  to  form  an  insoluble  compound,  forming  a colored 
scum  on  top  of  the  dye-vat.  This  substance,  called  by  the  Italian 
dyers  lacca,  was  collected,  dried  and  sold  to  Artists  as  a pigment. 
Soon  the  natural  dyestuffs  were  found  to  yield  variously  colored 
lacca  and  methods  were  soon  developed  whereby  the  lakes  were  ob- 
tained direct  and  not  as  a residue  or  scum  of  the  dye-vat.  In  fact, 
today  the  manufacture  of  lake  colors  ranks  commercially  as  impor- 
tant as  the  dye  industry. 

A lake  pigment  is  not  simply  a mechanical  mixture  of  a base 
with  a dyestuff,  as  this  product  would  “bleed”  the  dye  in  water.  A 


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lake  which  has  the  dye  fixed  indelibly  on  a neutral  base  is  only  desir- 
able as  a pigment.  In  practice  the  neutral  base  on  which  the  dye- 
stuff is  fixed,  is  usually  Alumina,  Clay,  Barytes,  or  Paris  White. 

The  earlier  lakes  were  obtained  from  natural  coloring  matters, 
such  as  lac,  cochineal  (carmine),  Persian  berries,  Brazil  wood,  log- 
wood, etc.,  but  today  the  artificial  or  synthetic  dyestuffs  have 
almost  entirely  supplanted  the  natural  coloring  extracts,  yielding  in- 
numerable brilliant  colors,  most  of  which  are  only  of  sufficient  per- 
manence to  be  used  by  the  Artist  for  commercial  work,  if  at  all. 
Many  of  these  lake  colors  are  often  employed  to  give  stronger  color 
to  pigments,  but  their  addition  yields  but  temporary  brilliance. 

The  Artist  should  be  in  a position  to  roughly  detect  at  least  the 
addition  of  harmful  admixtures  to  his  colors,  as,  for  instance,  the 
addition  of  fugitive  dyes,  or  if  colors,  such  as  the  Cadmium  Yellows, 
have  been  adulterated  with  Chrome  Yellows,  or  whether  a pigment 
such  as  Cobalt,  for  which  he  pays  a big  price,  be  actually  pure 
Cobalt  and  not  a mixture  or  cheap  substitute,  or  likewise  if  Whites 
be  unadulterated  with  Chalk,  Clay,  Barytes,  etc.,  and  whether  a 
White  be  Zinc,  Lead,  etc. 

The  time  has  arrived  when  the  Artist  must  know  something  of 
the  composition  of  his  materials.  The  new . products  appearing 
yearly  only  tend  to  lead  into  difficulties,  unless  their  use  be  accom- 
panied with  the  proper  knowledge  of  their  properties.  Not  only  does 
the  student  or  Artist  owe  it  to  himself,  but  the  future  generations 
will  look  back  with  gratitude  when  examples  of  various  periods  re- 
main durable  throughout  the  ages. 

Why  in  this  one  profession  should  the  study  of  the  materials 
employed  in  the  various  techniques  be  so  often  thought  of  such  little 
importance?  We  stand  helplessly  by  and  witness  the  gradual  de- 
struction of  many  of  the  finest  examples  of  the  various  periods 
simply  because  the  respective  Artists  knew  nothing  of  the  dangers  of 
using  unstable  pigments,  oils,  etc.,  or  were  victims  of  the  alluring, 
brilliant,  unsafe  products  during  their  introduction.  We  may  ex- 
cuse the  Artist  of  former  times,  but  today  there  is  no  reason  why 
the  student  should  not  reflect  on  the  importance  of  preserving  his 
work  for  the  future.  Sometimes  the  improper  use  of  even  durable 
materials  has  caused  the  Artist  considerable  trouble. 

With  a few  bottles  of  reagents  tucked  away  in  the  studio,  the 
Artist  may  at  any  time  readily  test  any  color  in  question,  at  least 
for  harmful  adulterations  or  impurities.  I have  a book  now  in  press 


6 


(published  by  D.  Van  Nostrand  Co.,  New  York)  in  which  many  tests 
are  given  for  all  standard  pigments,  also  much  other  information  on 
pigments  of  interest  and  value  to  the  Artist,  student,  collector  and 
restorer,  which  I feel  should  fill  a long-felt  want. 

The  Artist  should  have  a small  bottle  each  of 

Alcohol — Denatured 
Sodium  Sulphide 

An  acid — Hydrochloric , Nitric  or  Sulphuric  Acid 
Ammonia  Water  or  a weak  solution  of  Caustic  Lye. 

The  alcohol  may  be  denatured  alcohol,  as  this  serves  the  purpose 
for  all  practical  needs.  It  is  used  to  detect  the  presence  of  adultera- 
tion with  dyes,  which,  if  soluble  in  alcohol,  will  color  the  alcohol. 
A color  when  treated  with  alcohol  or  water  which  does  not  stain 
these  liquids  would  indicate  no  water  or  alcohol  soluble  dyes  being 
present.  Some  dyes  require  a few  drops  of  ammonia  water  to  the 
alcohol  to  draw  them  from  the  pigment. 

If  the  pigment  be  in  dry  powder  form  it  need  but  be  shaken 
in  a small  bottle,  or  better  a test  tube,  together  with  a small  quantity 
alcohol.  Casually  the  color  which  the  Artist  examines  is  either  an  oil 
or  water  color.  Only  seldom  do  the  oils  or  gums  prevent  reaction 
of  the  above-named  reagents.  More  definite  results  are,  however, 
obtained  by  using  the  pigment  in  powder  form,  that  is  free  from 
oils,  or  gums,  etc.  Water  colors  are  easily  washed  free  of  these 
gums.  A small  quantity  of  the  color  is  placed  in  a small  container 
to  which  sufficient  water  is  added  to  make  a dilute  solution.  After 
thorough  shaking,  upon  leaving  the  pigment  settle,  the  water  should 
be  poured  off.  It  is  important  to  note  whether  the  water  has  become 
stained  with  color;  this  would  indicate  a partial  solution  of  the  pig- 
ment or  the  addition  of  water-soluble  dyestuff  to  the  pigment. 

Oil  colors  may  be  freed  from  oil  or  resins  by  washing  in  similar 
manner,  using  turpentine  in  place  of  water  and  then  removing  the 
turpentine  by  washing  with  alcohol.  If  the  alcohol  or  turpentine 
becomes  colored  it  would  indicate  adulteration  with  dyestuffs.  Some 
pigments  are  in  a very  fine  state  of  division  and  would  require  quite 
a time  to  settle,  therefore  much  time  may  be  saved  by  filtering  the 
pigment  from  the  turpentine  or  alcohol.  In  place  of  turpentine  other 
solvents  are  often  employed,  such  as  benzol,  toluol,  xylol,  ether, 
chloroform,  acetone,  amyl-acetate,  carbon  tetrachloride,  benzine,  etc., 


7 


etc.  Certain  colors,  such  as  Prussian  Blue,  have  such  strong  tinting 
strength  that  more  than  one  filtration  is  required  to  remove  the  finely 
divided  particles  from  the  solvent,  which  otherwise  may  mislead 
the  student  to  believe  that  the  discoloration  is  caused  by  dyes. 

Our  next  reagent  consists  of  a solution  of  about  one  ounce 
sodium  sulphide  in  a pint  of  water.  Sodium  sulphide  is  an  inexpen- 
sive chemical  and  is  used  principally  to  detect  the  presence  of  lead 
or  copper  in  pigments.  Such  pigments  as  the  White  Leads,  Flake 
White,  Cremnitz  White,  the  Chrome  Yellows,  Naples  Yellows,  Red 
Lead,  Orange  Mineral,  Chrome  Greens  (containing  Chrome  Yel- 
lows), Verdigris,  Malachite  Green.,  Emerald  Green,  or  any  other 
pigments  containing  lead  or  copper,  are  rapidly  turned  black  when  a 
drop  of  sodium  sulphite  solution  is  applied  to  them.  For  instance, 
if  any  Cadmium  Yellow  becomes  blackened  by  sodium  sulphide,  we 
immediately  suspicion  adulteration  with  Chrome  Yellows,  as  the 
Cadmiums,  when  pure,  should  not  become;  blackened.  Cadmium 
Orange  and  Cadmium  Red  may  show  adulteration  with  Red  Lead 
or  Chrome  Orange  if  blackened;  when  pure  both  are  not  discolored 
by  this  reagent.  Yellow  Ochre  should  remain  unaltered,  likewise 
the  genuine  Vermilions,  if  pure,  are  not  blackened  by  sodium  sul- 
phide. Any  of  the  green  pigments  turning  black  with  this  reagent 
would  indicate  either  Chrome  Yellows  or  Copper  Greens  to  be 
present.  Any  color  becoming  discolored  brown  or  black  with  sodium 
sulphide  should  not  be  used  by  the  Artist  desiring  complete  stability 
or  durability.  The  reaction  which  takes  place  with  this  reagent 
shows  exactly  what  will  occur  if  a painting  be  hung  where  sulphur- 
ous gases  come  in  contact  with  the  unprotected  pigment.  Many 
Artists  argue  that  in  their  experience  the  Chrome  Yellows,  Flake 
Whites  or  White  Leads  have  not  shown  discoloration  for  a number 
of  years  and  would  no  doubt  continue  to  remain  unchanged.  This 
may  be  true  in  the  case  of  the  White  Leads,  but  only  under  one 
condition,  and  that  is,  that  the  pigment  be  properly  protected  from 
impure  air  by  an  application  of  varnish  or  other  means.  White 
Leads  are  perfectly  permanent  to  light  and  very  desirable  if  prop- 
erly used.  On  the  other  hand,  this  can  not  be  said  of  the  Chrome 
Yellows,  as  we  will  learn  when  speaking  later  of  these  pigments. 
The  same  is  also  true  of  the  Chrome  Greens  (not  to  be  confused  with 
the  Oxide  of  Chromium  Greens,  such  as  Emeraude  Green  or 
Viridian,  which  are  extremely  stable  pigments),  Verdigris,  Malachite 
Green,  etc. 


8 


A bottle  of  any  acid,  such  as  hydrochloric  acid,  which  I usually 
prefer,  or  sulphuric  acid  or  nitric  acid,  is  useful  in  testing  certain 
colors.  Cobalt  Blue,  Cerulean  Blue,  Emeraude  Green,  Viridian, 
Permalba,  Vermilions,  Prussian  Blue,  Cobalt  Violets,  all  Blacks  (ex- 
cept Ivory  Black,  which  is  partly  soluble  in  acid),  are  indifferent  to 
dilute  acids  and  any  change  taking  place  would  indicate  the  pigment 
to  be  impure  or  adulterated. 

A solution  of  a base,  such  as  caustic  lye  or  ammonia  water, 
serves  to  determine  purity  and  adulteration  of  pigments,  which 
should  remain  unaffected  by  these  alkalies. 

The  pigment  of  which  the  Artist  uses  a larger  amount  than  of 
any  other,  is  White.  The  three  principal  Whites  are  the  Lead 
Whites  ( Flake  and  Cremnitz) , Zinc  White  and  Permalba. 

The  Lead  Whites  (basic  lead  carbonates)  were  employed  by  the 
Egyptians.  There  is  and  always  has  been,  much  controversy  on  the 
use  of  these  pigments  in  the  Fine  Arts. 

We  only  too  often  wrongly  accuse  Lead  Whites  of  being  unde- 
sirable pigments.  It  must  be  said  in  their  favor  that  when  used 
properly  the  Lead  Whites  are  very  durable  and  permanent  pigments. 
The  sensitiveness  of  the  Lead  Whites  toward  sulphur  compounds 
and  gases  (which  tend  to  convert  the  lead  to  black  lead  sulphide) 
makes  the  proper  use  of  these  Whites  very  important.  Unfortu- 
nately the  opacity  of  the  Lead  Whites  has  done  much  to  make  these 
pigments  almost  too  popular.  The  Artist  using  Flake,  Cremnitz  or 
White  Lead  for  underpainting,  could  not  get  a more  desirable  pig- 
ment for  this  purpose,  as  here  the  color  is  properly  protected  from 
impure  air  contaminated  with  sulphurous  gases.  But  where  these 
pigments  are  used  and  left  exposed,  it  is  only  a matter  of  time, 
depending  on  how  impure  the  atmosphere  in  which  the  painting  is 
placed,  that  discoloration  will  occur.  An;  application  of  varnish 
will  considerably  protect  and  retard  this  reaction.  White  Leads  also 
tend  to  reduce  most  organic  pigments  in  mixtures  and  should  not 
be  employed  together  with  impure  Cadmium  Yellows,  Vermilions, 
Ultramarines,  etc.  The  tinting  value  of  the  White  Leads  does  not 
approach  that  of  Zinc  Whites  or  Permalba.  White  Lead  is  a cumu- 
lative poison.  A simple  test  for  White  Lead  is  the  black  discolora- 
tion when  treated  with  sodium  sulphide.  In  most  acids  White  Lead 
dissolves  with  strong  effervescence.  When  strongly  heated,  it  turns 
from  yellow  to  red  color.  In  these  three  latter  respects  it  differs 


9 


from  Zinc  White,  which  dissolves  without  effervescence  in  acid  and 
upon  heating  turns  yellow;  but  upon  cooling,  again  turns  white. 
Nitric  acid  or  acetic  acid  entirely  dissolves  White  Lead;  any  insolu- 
ble residue  would  indicate  admixture  with  such  materials  as  clay, 
barytes,  silica,  etc.  Caustic  lyes  also  dissolve  White  Leads.  White 
Leads  in  oil  dry  well,  yielding  an  elastic  and  tough  film.  Owing  to 
their  sensitiveness  to  impure  air  White  Leads  are  not  practically 
adaptable  to  other  painting  techniques. 

A'  very  popular  pigment  is  found  in  Zinc  White , the  use  of 
which  as  a pigment  dates  from  the  latter  part  of  the  eighteenth 
century.  Zinc  White  is  the  oxide  of  the  metal  zinc  and  like  many 
other  pigments  was  too  severely  criticized  during  the  years  follow- 
ing its  introduction.  The  impure  condition  of  these  Zinc  Whites 
did  much  to  destroy  the  confidence  which  should  be  placed  in  this 
desirable  pigment  when  pure.  Today  the  American  Zinc  Whites! 
can  not  be  excelled  for  their  dependable  purity  and  consequent  sta- 
bility as  a pigment.  Pure  Zinc  Whites  are  very  permanent  under 
all  ordinary  conditions  of  painting.  When  ground  in  oil,  they  dry 
more  slowly  than  the  Lead  Whites  and  yield  a much  harder  film. 
In  fact,  it  is  to  be  advised  against,  painting  Zinc  Whites  too  impasto, 
the  application  tending  to  become  horny  and  friable  upon  ageing. 
The  tinting  power  of  Zinc  White  is  very  high.  Sodium  sulphide  so- 
lution does  not  discolor  this  pigment. 

I have  introduced  in  recent  years  a pigment  which  bids  fair 
to  become  one  of  the  most  desirable  Whites  for  Artists’  use.  This 
pigment,  called  Permalba , does  not  contain  either  lead  or  zinc  and 
is  unaffected  by  all  ordinary  chemical  reagents,  remaining  unchanged 
under  all  conditions  of  painting.  The  high  tinting  value  and  excep- 
tional opacity,  together  with  its  stability  and  inertness  toward  all 
other  pigments  in  mixtures,  in  all  painting  techniques,  ranks  Per- 
malba as  an  ideal  Artists’  White.  In  oil,  Permalba  requires  about 
the  same  time  as  Zinc  White  to  dry,  yielding  a very  flexible  and 
durable  film.  Permalba  has  gone  through  a very  thorough  experi- 
mental stage,  ranging  over  a number  of  years,  and  has  been  found  to 
remain  permanent  under  all  conditions  of  painting.  Its  insolubility 
in  acids  and  alkaline  reagents  which  dissolve  Whites  of  lead  or  zinc 
composition,  readily  distinguishes  Permalba  from  these. 

The  most  important  Red  Pigments  are  the  Alizarin  Madder  and 
Genuine  Madder  Lakes,  Genuine  Vermilions,  Red  Ochres  and  Red 
Iron  Oxides. 


10 


The  Alizarin  Madder  as  also  the  genuine  Madder  Lakes  derive 
their  color  from  Alizarin,  which  today  is  prepared  from;  anthracene, 
a derivative  of  coal-tar.  The  ancients  already  obtained  this  product 
as  an  extract  from  the  root  of  the  madder  plant,  in  which  it  is 
usually  associated  with  the  less  permanent  and  more  purple  in  hue 
Purpurin.  The  synthetic  product  is  produced  today,  so  that  a very 
pure  and  dependable  pigment  is  obtained,  equal,  and  in  some  in- 
stances better,  than  the  natural  color  extract.  The  Alizarine  Mad- 
ders or  modifications  of  these  colors  appear  commercially  as  Alizarin 
Crimson,  Alizarin  Madder,  Rose  Madders,  Madder  Lakes,  Pink 
Madder,  Brown  Madder,  etc. 

The  Alizarin  Madders  are  insoluble  in  water  or  alcohol,  which 
distinguishes  them  from  most  of  the  ordinary  organic  dyestuffs, 
which  impart  color  to  these  liquids.  The  Alizarin  Madders  are  best 
used  as  overglaze  colors  and  mixture  with  Chrome  Yellows,  Lead 
Whites,  Flake  White,  Yellow  Ochre  and  Raw  Earth  Colors  are 
best  regarded  as  being  of  uncertain  stability.  Mixtures  with  dura- 
ble pigments  such  as  the  Cadmiums,  Permalba,  Burnt  Ochres,  Red 
Oxides,  Emeraude  Green,  Cobalt  Blue,  Ultramarine,  all  Blacks,  etc., 
show  high  stability. 

The  Genuine  Vermilions  are  compounds  of  the  elements  sul- 
phur and  mercury  (quick-silver),  and  were  known  and  used  400 
B.  C.  by  the  Egyptians  and  early  Chinese.  Pliny,  A.  D.  77,  refers 
to  them  as  minium,  a name  now  given  to  Red  Lead.  In  more 
modern  times  the  Vermilions  are  offered  often  very  impure,  some- 
times containing  an  excess  of  sulphur,  etc.,  and  these  impurities  are 
principally  responsible  for  the  bad  reputation  the  Vermilions  re- 
ceive. When  the  Vermilions  are  pure,  no  discoloration  should  take 
place  in  mixture  with  pure  Flake  Whites.  They  are  very  durable 
in  mixtures  with  other  stable  pigments  and  are  not  affected  by  im- 
pure air,  sulphurous  gases  or  sodium  sulphide.  A black  discolora- 
tion would  indicate  admixture  with  Red  Lead  or  Chrome  Red  or 
Orange  upon  treating  Vermilions  with  the  sodium  sulphide  solu- 
tion. Alcohol,  water,  weak  acids  or  alkalies  should  not  react  with 
genuine  Vermilions.  When  strongly  heated,  Vermilions  sublime, 
leaving  but  a trace  of  residue.  A large  amount  of  residue  would 
indicate  adulteration  with  red  lead,  clay,  barytes,  etc. 

For  some  inexplicable  reason  some  varieties  of  Vermilions 
darken  somewhat  on  long  exposure  to  direct  sunlight,  especially  is 
this  evident  with  impure  Vermilions.  Vermilions,  when  overpainted 


11 


with  Alizarin  Madder,  have  shown  greater  permanence  under  pro- 
longed exposure  to  direct  sunlight  than  when  used  alone. 

The  Red  Iron  Oxides  and  Red  Ochres,  such  as  Indian  Red , 
Venetian  Red,  Light  Red,  etc.,  receive  their  color  from  the  oxides  of 
iron,  principally  ferric  oxide.  The  natural  and  artificial  ochres  are 
practically  alike  fin  properties,  resisting  dilute  acids  and  alkalies  and 
showing  no  discoloration  with  sodium  sulphide  solution.  These 
pigments  were  used  in  all  techniques,  from  early  times. 

Most  of  the  modern  exceedingly  brilliant  Red  Lakes  appearing 
under  many  fanciful  names,  although  of  considerable  value  for  com- 
mercial work,  are  not  desirable  for  absolute  permanency.  The 
Artist  had  better  acquaint  himself  with  the  durability  of  the  pig- 
ment in  question,  from  the  manufacturer  of  the  respective  color 
when  desiring  to  use  such  as  the  Geranium  Lakes,  Scarlet  Lakes, 
Brilliant  Lakes,  etc. 

Carmine  need  not  be  discussed  as  it  should  not  be  employed, 
except  for  limited  durability,  as  in  commercial  work. 

The  most  important  yellow  pigments  are  the  Cadmium  Y ellows, 
which  are  all  compounds  of  the  elements,  cadmium  and  sulphur. 
When  pure,  these  yellows,  ranging  from  a pale  yellow  to  deep 
orange,  are  permanent  to  light,  not  affected  by  sulphurous  gases  or 
compounds  and  are  durable  in  mixtures  with  other  dependable  pig- 
ments. An  exception  of  this,  however,  is  found  with  Emerald 
Green  and  Cadmium  Yellow  in  mixture.  These  two  colors  are  not 
compatible  and  should  never  be  used  together.  Chrome  Yellows 
frequently  are  used  to  adulterate  Cadmium  Yellows,  the  detection 
of  which  is  readily  discovered  by  treating  the  color  with  sodium 
sulphide,  when,  if  Chrome  Yellows  are  present,  the  sample  will  turn 
brown  or  black.  Pure  Cadmium  Yellows  are  not  discolored  by  this 
reagent.  In  concentrated  hydrochloric  acid  the  Cadmium  Yellows 
should  be  entirely  soluble,  leaving  no  residue. 

Chrome  Yellows  ranging  in  color  from  a pale  yellow  to  deep 
orange  are  essentially  compounds  of  lead  chromate  and,  like  all  pig- 
ments containing  lead,  they  are  very  sensitive  to  sulphurous  gases 
and  compounds.  Not  only  are  the  Chrome  Yellows  blackened  by 
sulphur,  but  under  exposure  to  direct  sunlight  they  invariably  turn 
brownish ; especially  is  this  evident  when  the  pigment  is  not  chemi- 
cally pure.  Chrome  Yellows  are  likewise  not  compatible  in  mixtures 
with  most  organic  and  lake  colors.  There  are  many  Artists  using 
Chrome  Yellows  who  should  first  apply  some  of  the  simple  tests  for 
durability  before  placing  undue  reliance  in  their  permanency. 


12 


Indian  Yellow  is  a transparent  color  of  good  permanence  and 
stability  in  mixture  with  most  durable  pigments. 

There  are  several  Yellow  Lake  pigments,  the  coloring  principal 
of  which  is  derived  from  coal-tar,  which  are  being  accepted  in 
place  of  the  genuine  Indian  Yellow.  These  colors  are  also  very 
permanent  and  especially  useful  as  overglazing  colors. 

The  Lemon  Yellows  ( Barytes  Yellow , Strontian  Yellow,  and 
Zinc  Yellow ) are  very  useful,  and  when  pure  have  proven  to  pos- 
sess considerable  permanence.  The  further  discussion  of  these  pig- 
ments, as  also  the  Cobalt  Yellow,  Naples  Yellow,  etc.,  must  be  taken 
up  later. 

Of  the  green  pigments,  unquestionably  the  Transparent  Oxide 
of  Chromium,  also  known  as  Emeraude  Green  and  Viridian,  is  the 
most  desirable,  possessing  complete  stability  in  all  techniques  and 
remaining  durable  together  with  other  pigments  in  mixtures.  Adul- 
terations are  readily  detected,  as  the  pigment  should  remain  un- 
affected upon  treating  with  acids,  or  alkalies,  or  sodium  sulphide. 
Any  discoloration  would  indicate  admixtures.  Water  or  alcohol  will 
extract  any  dyestuffs.  Of  equal  durability  is  the  Opaque  Oxide  of 
Chromium,  which,  although  possessing  identical  chemical  proper- 
ties as  the  transparent  variety,  does  not  possess  the  strength  of 
color,  being  a mat,  dull  green. 

Emerald  Green  is  a pigment  which  is  practically  permanent  to 
light,  but,  being  sensitive  to  sulphurous  gases  and  compounds,  must 
be  properly  protected  from  these  to  insure  stability.  With  most 
durable  pigments  Emerald  Green  is  stable  in  mixtures,  the  principal 
exception  being  with  the  Cadmium  Yellows.  When  Emerald  Green 
is  used,  it  is  advisable  to  use  the  pigment  alone,  as  in  mixtures  it  has 
but  little  tinting  strength  and  any  danger  of  incompatibility  is  then 
removed.  The  pigments  which,  like  Emerald  Green,  contain  copper, 
are,  however,  best  avoided  by  the  Artist.  To  this  group  belong  such 
colors  as  Malachite  Green,  Verdigris,  and  the  blue  copper  pigments. 
They  are  sensitive  to  sulphur  and  unstable  in  mixtures  with  other 
pigments. 

Another  set  of  very  durable  green  pigments  are  the  Cobalt 
Greens.  They  are  of  weak  tinting  strength,  but  are  exceedingly  per- 
manent to  light  and  air  and  with  other  colors  in  mixtures.  Sodium 
sulphide  solution  does  not  blacken  these  greens. 

The  green  lake  pigments  do  not  form  an  important  group,  most 
of  these  being  only  successfully  employed  for  commercial  purposes. 


13 


Usually  the  Artist  may  prepare  his  own  greens  on  the  palette,  using 
Cobalt  Blue,  Ultramarine  or  Prussian  Blue  with  the  Cadmiums,  etc. 

The  principal  blue  pigments  are  Cobalt  Blue , Ultramarines  and 
Prussian  Blue.  All  of  these  colors  are  very  permanent  to  light,  in- 
soluble in  water  or  alcohol  (detection  of  dyes)  and  durable  in  mix- 
tures with  other  stable  pigments.  Cobalt  distinguishes  itself  from 
the  other  two  in  being  insoluble  in  acids  and  alkalies.  Ultramarines 
( New  Blue , Permanent  Blue,  French  Blue),  are  destroyed  by  acids. 
Prussian  Blue  resists  dilute  acids  but  is  discolored  by  lyes,  for  this 
reason  can  not  be  used  as  a Fresco  color.  Sodium  sulphide  will  not 
blacken  these  blues,  discoloration  would  indicate  adulteration  with 
copper  blues. 

The  Cobalt  Violets  possess  the  strongest  color  of  the  durable 
violet-hue  pigments.  They  are  perfectly  permanent  to  light,  being 
also  indifferent  towards  acids,  alkalies  and  sodium  sulphide.  These 
properties  readily  distinguish  it  from  the  very  fugitive  aniline  lake, 
Mauve.  Mauve  and  Magenta  are  very  strong  colors  but  much  too 
fugitive  for  Artists’  use.  Violets  and  purples  may  be  easily  mixed  on 
the  palette,  using  Cobalt  or  Ultramarine  with  Alizarin  Madder. 

The  natural  and  artificial  ochres  and  umbers  are  the  most  desir- 
able brown  pigments.  Yellow  Ochre,  Roman  Ochre,  Transparent 
Golden  Ochre,  Raw  Sienna,  and  Razo  Umber  are  natural  earth  pig- 
ments deriving  their  color  from  oxides  and  hydrates  of  iron.  The 
artificial  ochres  are  called  Mars  Yellozv,  Mars  Orange,  Mars  Red, 
etc.  Both  the  native  and  artificial  products  are  very  durable  in  all 
techniques  and  may  be  successfully  used  in  mixtures  with  other 
stable  pigments.  Mixtures  of  lake  colors  and  organic  pigments  with 
the  raw  earth  colors  are  best  regarded  as  being  of  questionable  sta- 
bility. When  these  raw  earths  are  calcined,  they  take  on  a decided 
red  hue  and  are  then  dependable  in  mixture  with  all  other  pigments, 
being  equally  permanent  to  light  and  air,  as  the  raw  earths.  They 
resist  alkalies  and  are  only  slowly  acted  upon  by  strong  acids.  Raw 
Sienna  and  Yellow  Ochre  are  sometimes  toned  with  Chrome  Yellow, 
the  detection  of  which  is  evident,  if  the  pigment  is  blackened  by 
sodium  sulphide  solution. 

Bitumen  or  Asphaltum  should  not  be  used  by  the  Artist  desiring 
permanency.  The  colors  are  of  organic  origin,  composed  of  a va- 
riety of  pitchy,  tarry  substances  which  partly  decompose  under  expos- 
ure to  direct  sunlight.  As  oil  colors,  they  are  exceedingly  slow 
dryers,  and  even  after  years  they  soften  and  “bleed”  or  diffuse 


A 


14 


through  overlying  layers  of  paint.  Heavy  applications  readily  cause 
cracking.  Vandyke  Brown , also  being  partly  composed  of  bitumen- 
ous  matter,  is  unsafe  for  durability,  fading  to  a cold  grey  tone  under 
exposure  to  direct  sunlight  and  should  be  replaced  by  Burnt  Umber 
with  Ivory  Black. 

All  the  black  pigments  ( Lamp  Black , Blue  Black , and  Ivory 
Black ) are  very  permanent  and  durable  colors,  resisting  both  acids 
and  alkalies.  With  all  other  pigments  they  are  safe  in  admixtures. 
With  exception  of  Ivory  Black,  they  are  all  principally  composed  of 
carbon.  Ivory  Black  contains  a varying  percentage  of  bone  ash; 
is  in  consequence  partly  soluble  in  acids,  but  is  a better  dryer  in  oil 
than  the  Lamp  Blacks. 

Oils,  Varnishes,  Siccatifs  and  Mediums. 

I have  found  many  Artists  who  were  exceedingly  conscientious 
in  their  selection  of  durable  pigments,  displaying  a complete  lack 
of  technical  knowledge  of  the  vehicles  they  employ.  The  vehicles 
and  mediums  used  in  the  various  techniques  are  just  as  essential 
for  permanency  and  durability  as  are  the  pigments. 

Let  us  first  consider  the  importance  of  the  proper  oils  used  in 
Oil  Paintings.  For  the  Artist,  oils  may  be  generally  divided  into 
three  principal  groups: 

i.  Drying  Oils : such  as  Linseed  and  Poppy  Oil. 

I 2.  Semi-  or  Slow-drying  Oils : such  as  Sesame,  Cottonseed  Oil. 

3.  Non-drying  Oils:  such  as  Olive  Oil,  Castor  Oil,  Cocoanut 

| Oil. 

The  oils  obtained  from  the  animal  kingdom  are  not  practically 
adaptable  for  use  in  the  Fine  Arts. 

Only  few  of  the  volatile  mineral  oils,  the  lighter  fractions  of 
petroleum,  such  as  Benzine,  Naphtha,  Gasoline,  Petroleum  ether, 
and  sometimes  Coal  Oil  may  be  used,  but  then  only  when  their  use  be 
thoroughly  understood.  They  find  wider  application  as  solvents  for 
resins,  as  also  do  the  lighter  fractions  of  coal-tar,  such  as  benzol, 
coal-tar  naphtha,  toluol,  xylol,  etc. 

We  must  leave  the  discussion  of  oils,  varnishes,  etc.,  for  a later 
time,  as  this  subject  is  as  comprehensive  as  the  matter  on  pigments 
and  must  be  taken  up  in  detail  as  it  is  of  much  importance.  We  will 
therefore  now  mention  only  the  most  interesting  facts. 

The  two  principal  drying  oils,  we  have  said,  were  Linseed  Oil 


15 


and  Poppy  Oil.  By  drying  we  mean  that  these  oils  absorb  oxygen 
from  the  air,  thereby  becoming  converted  into  a solid,  tough,  elastic, 
transparent  mass.  This  form  of  drying  may  be  contrasted  to  the 
manner  in  which  such  substances  as  turpentine  and  the  lighter  frac- 
tion of  the  mineral  oils  dry.  These  latter  dry  by  evaporation.  This 
may  be  readily  illustrated  by  placing  a small  known  quantity  of  lin- 
seel  oil  in  an  open  container  and  an  equal  amount  of  turpentine  in 
another  open  container.  After  several  days  it  will  be  noticed  upon 
weighing  each  container  that  that  which  contains  the  linseed  oil  will 
have  increased  in  weight  about  io  per  cent.,  whereas  that  which  con- 
tained the  turpentine  will  be  practically  empty.  Again,  upon  closely 
examining  the  oil,  we  will  find  the  mass  to  have  dried  with  a con- 
siderably wrinkled  surface  (usually  to  be  seen  also  on  old  cans  of 
heavy  paint  which  have  stood  open  for  a prolonged  time). 

The  oils  belonging  to  the  semi-  and  non-drying  group,  distinguish 
themselves  from  the  drying  oils  in  that  they  do  not  absorb  oxygen 
from  the  air  in  such  a degree  as  the  drying  oils  and  during  their 
drying  become  partly  rancid  and  do  not  yield  tough,  elastic,  durable, 
transparent  films,  as  do  the  drying  oils.  Linseed  and  Poppy  Oils 
have  been  in  use  for  several  centuries  and  have  proven  conclusively 
their  importance  as  painting  oils  and  the  Artist  who,  without  fur- 
ther inquiry,  makes  use  of  the  non-drying  oils  such  as  olive  oil,  castor 
oil,  cocoanut  oil,  etc.,  is  doing  himself  and  his  work  a great  injustice. 

Why  do  so  many  Artists  believe  to  make  remarkable  discov- 
eries by  employing  such  oils  with  waxes,  varnishes,  and  strong  Sic- 
catifs,  and,  as  I have  known,  some  to  use  even  vaseline  with  their 
colors  ? 

I must  postpone  explanation  why  the  use  of  improper  oils  has 
caused  the  destruction  of  many  works  of  art,  it  requiring  further 
explanation  of  the  composition  of  these  products  in  order  to  more 
clearly  understand  their  properties. 

Linseed  Oil  and  Poppy  Oil  differ  somewhat  in  the  time  required 
to  dry,  Poppy  Oil  drying  somewhat  slower.  Raw  Linseed  Oil  con- 
tains a natural  coloring  matter  which  is  somewhat  objectionable  to 
Artists,  especially  for  delicate  tints  and  for  whites.  These  colors, 
when  ground  in  Poppy  Oil,  do  not  show  this  yellow  cast.  When 
Linseed  Oil  is  exposed  to  direct  sunlight  this  coloring  matter  is 
bleached,  but  returns  when  the  oil  is  again  placed  in  the  dark.  Com- 
mercially, Linseed  Oil  is  bleached  by  different  methods  and  must 
be  thoroughly  washed  free  from  the  acid,  etc.,  used  in  this  process, 


16 


in  order  to  be  desirable  for  Artists’  use.  I wish  to  particularly  warn 
the  Artist  against  the  use  of  anything  but  the  purest  Linseed  Oil  or 
Poppy  Oil,  which  have  proven  their  merits  so  successfully  in  past 
years. 

Turpentine , which  is  obtained  by  redistillation  of  exudations  of 
various  pine  trees,  is  a very  thin,  volatile,  colorless  liquid  used  gen- 
erally in  conjunction  with  oils  or  as  a solvent  for  resins.  It  is  one 
of  the  most  useful  vehicles  in  oil  painting. 

The  early  painters  had  already  discovered  that  by  boiling  lin- 
seed oil  together  with  finely  divided  lead  or  lead  compounds,  a prod- 
uct was  obtained  which  dried  more  quickly  than  the  raw  oil.  To- 
day many  such  compounds  are  made,  some  using  lead,  manganese, 
and  in  late  years  cobalt  compounds,  to  produce  Siccatifs  which  are 
very  quick  drying  compounds.  The  use  and  abuse  of  Siccatifs  re- 
quires lengthy  explanation  and  cannot  be  discussed  at  this  time.  I 
do,  however,  wish  to  warn  the  Artist  against  their  use,  except  for 
commercial  work  where  durability  and  permanence  is  of  secondary 
importance.  It  will  usually  be  found  the  speed  with  which  a paint 
film  is  forced  to  dry  by  their  use  consistently  subtracts  from  the 
durability  of  the  painting,  not  even  to  mention  the  possible  develop- 
ment of  cracks  and  rapid  darkening  ensuing  from  excess  use. 

There  are  three  resins  which  find  widest  application  in  the  Fine 
Arts,  they  are  Mastic , Damar,  and  Copal.  The  Mastic  resin  is 
soluble  in  turpentine,  as  is  also  the  Damar.  The  Copals  distinguish 
themselves  from  these  in  being  practically  insoluble  in  most  ordinary 
solvents,  requiring  special  treatment  to  yield  varnishes  of  the  highest 
durability.  The  usual  method  employed  in  preparing  Copal  Varnishes 
consists  in  heating  the  resin  together  with  linseed  oil  and  turpentine 
and  frequently  the  addition  of  drying  compounds  give  quicker  dry- 
ing Copal  Varnishes.  Copal  Varnishes  yield  upon  drying  the  most 
durable  protective  films,  but  on  account  of  the  manner  in  which 
they  resist  all  ordinary  solvents,  they  are  very  tedious  for  the 
restorer  to  remove  after  ageing,  thereby  endangering  the  underneath 
painting.  Mastic  Varnish  can  readily  be  removed  from  aged  paint- 
ings with  ordinary  solvents,  such  as  turpentines,  etc.,  as  can  also 
Damar  Varnish,  and  should  for  this  reason  not  be  employed  together 
with  the  painting  oils  while  painting. 

Any  questions  which  the  Artist  or  student  may  desire  to  ask 
will  be  very  welcome,  as  it  is  his  only  means  of  obtaining  informa- 
tion which  I feel  may  mean  much  to  him  later. 

F.  W.  WEBER. 


Form  481-OM323 


